Tens of thousands of Egyptian protesters defied a curfew for a third day and gathered in the heart of the ancient city of Cairo, decades of humiliation and economic stagnation fueling loud cries of "revolution" and "down, down with Hosni Mubarak!"

Now Nobel Prize winner Mohamed ElBaradei faces a pivotal moment. Mr. ElBaradei said earlier today he had rallied Egypt's opposition and democracy forces -- from the Muslim Brotherhood to the secular Kifaya democracy movement -- behind him, and called for Mubarak's immediate resignation. The Muslim Brotherhood confirmed it was backing ElBaradei to enter into negotiations to manage a transition.

Reporters on the ground say ElBaradei has reached Tahrir (Liberation) Square in the heart of Cairo and if he can demonstrate that the tens of thousands gathered there are behind him (very much an open question since he has no political network of his own, has lived mostly outside of the country for the past decade, and it's unclear if the logistics of standing up a strong enough public address system can be worked out) it will be harder for Mubarak to hang on -- or to hand power to Mr. Suleiman in a soft, military backed coup.

Will ElBaradei be a credible face for a popular uprising that many protesters on the streets of Cairo and activists are now calling a "revolution?" The spontaniety of the uprising, inspired by Tunisia that became like a dam breaking through the fear of the Egyptian populous, has left this a largely leaderless movement so far. Both the organized supporters of democracy in Egypt and the Mubarak regime are trying to grab a tiger by the tail. This evening in Cairo is ElBaradei's first shot at seizing control of and directing Egypt's street power.

"We want to see this peaceful uprising on the part of the Egyptian people to demand their rights to be responded to in a very clear, unambiguous way by the government, and then a process of national dialogue that will lead to the changes that the Egyptian people seek and that they deserve," Secretary of State Clinton told CNN. "What we're trying to do is to help clear the air so that those who remain in power, starting with President Mubarak, with his new vice president, with the new prime minister, will begin a process of reaching out, of creating a dialogue that will bring in peaceful activists and representatives of civil society to, you know, plan a way forward that will meet the legitimate grievances of the Egyptian people."

Reporters in Tahrir Square say that Mubarak "remaining in power" may not cut it. "People are occupying every corner of the square engaged in discussion with the army soldiers trying them to bring them over to their side," Hossam Hamalawy, an Egyptian activist and journalist, told Al Jazeera English on the phone from Tahrir shortly before ElBaradei was reported to have arrived. "We do not want Omar Suleiman or other figures connected with the regime to continue. The military has been ruling Egypt since 1962 and we don’t want the military in the freedom arena."

Suleiman is a former senior officer, as is Ahmed Shafiq, who Mubarak named new prime minister yesterday in an attempt to take the air out of the protests.

Issandr El Amrani, an analyst of Egyptian politics who runs the Arabist website, told AJE from Tahrir Square as ElBaradei arrived that protester demands are clear.

“They want to have clean and fair elections, they want to be able to chose their governments. They understand there will have to be a transition period, but they want it to end with elections," he said. "We don’t know who has real authority today whether it’s President Mubarak or his vice president… we don’t know who’s in charge. Right now, the military is in charge, the tanks are on the street."